Frostburg mining journal. [volume] (Frostburg, Md.) 1871-1913, 1887-08-27

well understood. We are all famil-
lar with the dust-whirls that fire.
quently start up in our streets and speed
lily expend their little energy. They are
the result of the encounter of two small
opposing currents of air. From the
small we learn of the great. Now, let
us look for moment at the cause of our
frequently tumultuous sea of air, the
hills and the hollows, upon which
weather prediction is founded.
Unlike the majestic circuit over the
inter-tropical regions, called the trade
and the anti-trade winds, the opposite
currents over the middle ATTITUDES, COM
monty known as the equatorial and the
polar currents, skim along nearer the
earth, frequently intermingle and by
reason of their different characters pro-
duce atmospheric disturbances, some
times purely local, as the tornado and
thunderstorm, and sometimes covering
vast areas of the earths surface, as in
cyclones. In our ATTITUDES the general
surface or equatorial current coming
from the Gulf of Mexico and the South
ern seas is warm and humid; the upper
return or polar current coming from the
polar regions is cold and dry. These
two opposite currents of the middle lati-
tudes are the theatre of our weather-its
changes and phenomena.
Solar heat is the prime disturbing force,
and the air which is heated mainly at the
bottom of the atmospheric ocean ex-
pands, becomes Zig ter and ascends. This
isillustrated by the draught when we build
a fire in our CRATES. The heat of the fire
creates an upward current of air which,
were it not for the general law control
ling the motion of all liquids, would leave
a vacuum. The rarefaction and upris-
ing of a large body of air diminishes its
weight or pressure upon the earth which
the barometer reveals. AS the pressure
upon the mercury in the cistern of the
barometer is lessened, the column of mer-
curry in the tube sinks, and we call this
falling barometer. On the other hand, as
pressure upon the mercury in the cistern
increases, the column in the tube rises,
and this is a rising barometer. 1t may be
well to state that normal weight or press
ure of the atmosphere is when column
of air having the same base as the col
umn of mercury in the barometer sus-
tains the latter at the height of thirty
inches. When by reason of diminished
weight of air the column of mercury sinks
considerably below that, it is called a
low, and when, by reason of increased
weight of air, it rises in the tube consid
erably above that, 1t is called a high
barometer.
Now, when heated, vaporiZed air of
the lower strata of the atmosphere rises
| and enters the upper strata, where the
cold return or polar current flows along
in an opposite direction, whirl or gyra-
ton is initiated This results in circu-
lar movement, having for its centre the
area where the pressure is least. The
initial gyration being established, ex-
tends downward and in all directions
and moves forward upon the surface of
the earth as an area of circling winds,
called cyclone. The progressive move
ment of the cyclone is traced on the
weather maps from day to day, its con-
tour constantly changing. The cyclone
| is general movement of portion of
the atmosphere toward central area.
In this movement the wind is DETECTED
! to the right, and this creates tendency
| to circulate around the centre with
spirally inward motion. In addition
to the upward movement, the centrifugal
force resulting from circulation about
centre still further diminishes the weight
or pressure of the atmosphere within the
central area. This upward movement of
| gions of cold air results in clouds and
finally rain, and the rain area, If it is of
any considerable extent, has an influence
upon the barometric depression or hollow
and upon the velocity and direction in
which it moves. Now, in the struggle
of the atmosphere for equilibrium the
heated, moist and light uprising air is
replaced by downpoIr of the cold, dry
and heavy air of the upper regions of
the atmosphere. This descending current
strikes the surface, heaping up and &C
;umulating, until there is what is tech
nically called an "area of high barome-
ter" or anti-cyclone. This downpour of
| the cold dry air of the upper regions,
started by the uprising of the warm light
surface air, may, perhaps somewhat in
| elegantly, be compared to stream of
sand falling from some elevation upon
the surface. If upon an uneven sur
race we pour stream of sand it will
form dome-like hill, down the sides or
slopes of which the sand particles will
flow with velocity according to the
character of the surrounding surface.
/ If there be a hollow at the base of this
/ sandhill, the sand particles on that side
will flow with greater rapidity and
( presently fill up the hollow.
( These hOllOWS and hills OF the atmOs-
phere are kept track of by the meteorolo-
gists, their changing contours and pro-
gressive movements delineated on the
weather map, and the various phases of
weather usually associated with them
announced in the daily "indications."
With knowledge of the elements of
meteorology, with numerous and frequent
reports of observations throughout the
country, and with some skill in the con-
struction and Interpretation of the
weather map, it would not seem to be
very difficult to foretell the weather of
to-day or tomorrow. There is no mys-
lery about it. Systematic and long-con-
tnued observation and careful compari
/ son have given us some important and
now well-established facts, from which
u few general laws have been formu-
lated. 1t may confidently be expected
that with enlarged experience and OBJ
servation system of deductive meteor
ology is possible in the future, whose
application to the forecasting of the
weather will be of failing practical
value. s. s. BAssLER.